The primary objective of this project is to define more precisely the acute and long-term actions of opiates on endocrine activities of the hypothalamic-pituitary-gonadal axis and to elucidate underlying biochemical mechanisms. Experiments with rats, in vivo and in vitro, are intended to follow up earlier studies with normal and opiate-addicted human subjects. In man, acute and chronic use of opiates lowers plasma testosterone levels, probably by inhibiting the hypothalamic secretion of luliberin (LRF), as indicated by a rapid suppression of lutropin (LH) release, a subsequent drop in plasma testosterone levels, and a normal LH response to LRF administration before or after an opiate. Naltrexone (a long-acting narcotic antagonist) not only blocks this inhibitory effect of opiates, but even in the absence of opiate drugs increases the mean plasma lutropin level, presumably because of endogenous opioid peptide blockade. Protracted supersensitivity to the lutropin stimulatory effect of naltrexone is indicated in abstinent opiate addicts. Experiments in vivo with catheterized rats are to be carried out for assessment of opiate effects on the episodic pulsatile secretion of pituitary, gonadal and adrenocortical hormones. Integrated blood samples are to be collected for hormone radioimmunoassay and bioassay. These studies are designed to elucidate the endocrine site(s) and mechanisms of opiate action in the whole animal using procedures that are not feasible with man. Experiments in vitro, with preparations of hypothalamic tissue, are designed to determine the relationships of opioid peptides, catecholamines, prostaglandins and steroid hormones in modulating the secretion of LRF. Beta-Endorphin, catecholamines, prostaglandins and LRF are to be analyzed by high performance liquid chromatography, radioimmunoassay and bioassay in medium obtained from superfusion of median eminence fragments.